/*---------------------------------------------------------------------------*/
static coffee_page_t
next_file(coffee_page_t page, struct file_header *hdr)
{
if(HDR_FREE(*hdr)) {
return (page + COFFEE_PAGES_PER_SECTOR) & ~(COFFEE_PAGES_PER_SECTOR - 1);
} else if(HDR_ISOLATED(*hdr)) {
return page + 1;
}
return page + hdr->max_pages;
}
/*---------------------------------------------------------------------------*/
static coffee_page_t
next_file(coffee_page_t page, struct file_header *hdr)
{
/*
* The quick-skip algorithm for finding file extents is the most
* essential part of Coffee. The file allocation rules enables this
* algorithm to quickly jump over free areas and allocated extents
* after reading single headers and determining their status.
*
* The worst-case performance occurs when we encounter multiple long
* sequences of isolated pages, but such sequences are uncommon and
* always shorter than a sector.
*/
if(HDR_FREE(*hdr)) {
return (page + COFFEE_PAGES_PER_SECTOR) & ~(COFFEE_PAGES_PER_SECTOR - 1);
} else if(HDR_ISOLATED(*hdr)) {
return page + 1;
}
return page + hdr->max_pages;
}
/*---------------------------------------------------------------------------*/
static coffee_page_t
get_sector_status(uint16_t sector, struct sector_status *stats)
{
static coffee_page_t skip_pages;
static char last_pages_are_active;
struct file_header hdr;
coffee_page_t active, obsolete, free;
coffee_page_t sector_start, sector_end;
coffee_page_t page;
memset(stats, 0, sizeof(*stats));
active = obsolete = free = 0;
/*
* get_sector_status() is an iterative function using local static
* state. It therefore requires that the caller starts iterating from
* sector 0 in order to reset the internal state.
*/
if(sector == 0) {
skip_pages = 0;
last_pages_are_active = 0;
}
sector_start = sector * COFFEE_PAGES_PER_SECTOR;
sector_end = sector_start + COFFEE_PAGES_PER_SECTOR;
/*
* Account for pages belonging to a file starting in a previous
* segment that extends into this segment. If the whole segment is
* covered, we do not need to continue counting pages in this iteration.
*/
if(last_pages_are_active) {
if(skip_pages >= COFFEE_PAGES_PER_SECTOR) {
stats->active = COFFEE_PAGES_PER_SECTOR;
skip_pages -= COFFEE_PAGES_PER_SECTOR;
return 0;
}
active = skip_pages;
} else {
if(skip_pages >= COFFEE_PAGES_PER_SECTOR) {
stats->obsolete = COFFEE_PAGES_PER_SECTOR;
skip_pages -= COFFEE_PAGES_PER_SECTOR;
return skip_pages >= COFFEE_PAGES_PER_SECTOR ? 0 : skip_pages;
}
obsolete = skip_pages;
}
/* Determine the amount of pages of each type that have not been
accounted for yet in the current sector. */
for(page = sector_start + skip_pages; page < sector_end;) {
read_header(&hdr, page);
last_pages_are_active = 0;
if(HDR_ACTIVE(hdr)) {
last_pages_are_active = 1;
page += hdr.max_pages;
active += hdr.max_pages;
} else if(HDR_ISOLATED(hdr)) {
page++;
obsolete++;
} else if(HDR_OBSOLETE(hdr)) {
page += hdr.max_pages;
obsolete += hdr.max_pages;
} else {
free = sector_end - page;
break;
}
}
/*
* Determine the amount of pages in the following sectors that
* should be remembered for the next iteration. This is necessary
* because no page except the first of a file contains information
* about what type of page it is. A side effect of remembering this
* amount is that there is no need to read in the headers of each
* of these pages from the storage.
*/
skip_pages = active + obsolete + free - COFFEE_PAGES_PER_SECTOR;
if(skip_pages > 0) {
if(last_pages_are_active) {
active = COFFEE_PAGES_PER_SECTOR - obsolete;
} else {
obsolete = COFFEE_PAGES_PER_SECTOR - active;
}
}
stats->active = active;
stats->obsolete = obsolete;
stats->free = free;
/*
* To avoid unnecessary page isolation, we notify the caller that
* "skip_pages" pages should be isolated only if the current file extent
* ends in the next sector. If the file extent ends in a more distant
* sector, however, the garbage collection can free the next sector
* immediately without requiring page isolation.
*/
return (last_pages_are_active || (skip_pages >= COFFEE_PAGES_PER_SECTOR)) ?
0 : skip_pages;
}
/*---------------------------------------------------------------------------*/
static coffee_page_t
get_sector_status(uint16_t sector, struct sector_status *stats)
{
static coffee_page_t skip_pages;
static char last_pages_are_active;
struct file_header hdr;
coffee_page_t active, obsolete, free;
coffee_page_t sector_start, sector_end;
coffee_page_t page;
memset(stats, 0, sizeof(*stats));
active = obsolete = free = 0;
if(sector == 0) {
skip_pages = 0;
last_pages_are_active = 0;
}
sector_start = sector * COFFEE_PAGES_PER_SECTOR;
sector_end = sector_start + COFFEE_PAGES_PER_SECTOR;
if(last_pages_are_active) {
if(skip_pages >= COFFEE_PAGES_PER_SECTOR) {
stats->active = COFFEE_PAGES_PER_SECTOR;
skip_pages -= COFFEE_PAGES_PER_SECTOR;
return 0;
}
active = skip_pages;
} else {
if(skip_pages >= COFFEE_PAGES_PER_SECTOR) {
stats->obsolete = COFFEE_PAGES_PER_SECTOR;
skip_pages -= COFFEE_PAGES_PER_SECTOR;
return skip_pages >= COFFEE_PAGES_PER_SECTOR ? 0 : skip_pages;
}
obsolete = skip_pages;
}
for(page = sector_start + skip_pages; page < sector_end;) {
read_header(&hdr, page);
last_pages_are_active = 0;
if(HDR_ACTIVE(hdr)) {
last_pages_are_active = 1;
page += hdr.max_pages;
active += hdr.max_pages;
} else if(HDR_ISOLATED(hdr)) {
page++;
obsolete++;
} else if(HDR_OBSOLETE(hdr)) {
page += hdr.max_pages;
obsolete += hdr.max_pages;
} else {
free = sector_end - page;
break;
}
}
skip_pages = active + obsolete + free - COFFEE_PAGES_PER_SECTOR;
if(skip_pages > 0) {
if(last_pages_are_active) {
active = COFFEE_PAGES_PER_SECTOR - obsolete;
} else {
obsolete = COFFEE_PAGES_PER_SECTOR - active;
}
}
stats->active = active;
stats->obsolete = obsolete;
stats->free = free;
return (last_pages_are_active || (skip_pages >= COFFEE_PAGES_PER_SECTOR)) ?
0 : skip_pages;
}
